1. Field of the Invention
The present invention relates generally to a power supply system and a method of controlling the same, and more particularly to a power supply system with an automatic transfer function and a method of controlling the same.
2. Description of Prior Art
An automatic transfer switch (ATS) is an electric switch that reconnects electric power source from its main power source to a backup power source. A power-supplying operation is transferred from the main power source to the backup power source by the automatic transfer switch so that stable power can be continually supplied to the protected equipment when the main power source occurs abnormal operations, such as insufficient power, interruption of power supply, and so on.
Reference is made to FIG. 1 which is a schematic circuit diagram of a prior art power supply system with an automatic transfer function. The power supply system is a dual power source power supply system. Note that, an automatic transfer switch apparatus 100 is adapted to transfer the two power sources to normally supply power to a load 74. That is, the power supply system includes a main power source V1, a backup power source V2, the automatic transfer switch apparatus 100, a main-power loop 71, a backup-power loop 72, and a load loop 73.
The automatic transfer switch apparatus 100 has a first switch 81, a second switch 82, a third switch 91, and a fourth switch 92. The first switch 81 is electrically connected to the main-power loop 71 and the second switch 82 is electrically connected to the backup-power loop 72. The third switch 91 has a first contact 91a, a second contact 91b, and a common contact 91c and the fourth switch 92 has a first contact 92a, a second contact 92b, and a common contact 92c. 
The first switch 81 is turned on, the common contact 91c of the third switch 91 is connected to the first contact 91a, and the common contact 91c of the fourth switch 92 is connected to the first contact 92a when the main power source V1 can normally supply power so that the main power source V1 supplies power to the load 74 via the main-power loop 71 and the load loop 73. On the other hand, the first switch 81 is turned off, the second switch 82 is turned on, the common contact 91c of the third switch 91 is connected to the second contact 91b, and the common contact 92c of the fourth switch 92 is connected to the second contact 92b when the main power source V1 cannot normally supply power so that the backup power source V2 supplies power to the load 74 via the backup-power loop 72 and the load loop 73. Therefore, a power-supplying operation is transferred from the main power source V1 to the backup power source V2 by the automatic transfer switch apparatus 100 so that stable power can be continually supplied to the protected equipment when the main power source V1 occurs abnormal operations, such as insufficient power, interruption of power supply, and so on.
For transmission and distribution operations of the power system, however, uncontrolled electric arc possibly carries some damage to rear-end electronic equipment in the transmission and distribution system. For example, uncontrolled electric arc, which is produced from by breaking or connecting switches, would melt switch contacts in distribution circuits so that the malfunctioned switches, the faulty electronic equipment, or even casualties could occur because of the switching failure between the main power source and the backup power source.
Accordingly, it is desirable to provide a power supply system with an automatic transfer function and a method of controlling the same are disclosed. Because the silicon-controlled rectifier (SCR) has the ability to bear large transient current but the mechanical relay has the limitation of mechanical lifetime, the SCRs are adapted to replace the mechanical relays to increase the reliability and coordination of transferring power supply between the main power source and the backup power source.